The effects of doping ions and doping rate on the structure, morphology and electrochemical performance of LiMxMn2-xO4, prepared via a batch hydrothermal synthesis process in supercritical water, were investigated. The structure, morphology and electrochemical performance of LiMxMn2-xO4 were characterized by XRD, SEM, and charge and discharge test, respectively. The results showed that: the cyclic performance of doping material improved in different degrees. Compared with material doping with Al and Fe, the material doping with Co has better performance: it has uniform particle size, good dispersity and stable electrochemical performance, and the amount doping of 5% is optimal value.

LiFexMn1−xPO4/C composites were synthesized by a solid-state reaction route using phenolic resin as both reducing agent and carbon source. The effect of Fe doping on the crystallinity and electrochemical performance of LiFexMn1−xPO4/C was investigated. The experimental results show that the Fe2+ substitution for Mn2+ will lead to crystal lattice shrinkage of LiFexMn1−xPO4/C particles due to the smaller ionic radii of Fe2+. In the investigated Fe doping range (x = 0 to 0.7), LiFexMn1−xPO4/C (x = 0.4) composites exhibited a maximum discharge capacity of 148.8 mAh/g at 0.1 C while LiFexMn1−xPO4/C (x = 0.7) composite showed the best cycle capability with a capacity retention ratio of 99.0% after 30 cycles at 0.2 C. On the contrary, the LiFexMn1−xPO4/C (x = 0.5) composite performed better trade-off on discharge capacity and capacity retention ratio, 127.2 mAh/g and 94.7% after the first 30 cycles at 0.2 C, respectively, which is more preferred for practical applications.

In this study, sub-micrometer LiFePO4 particles with high purity and crystallinity were synthesized using supercritical hydrothermal method as the cathode material for lithium ion batteries. Experimental results show that templates and calcination time have significant impacts on the purity, particle size and morphology of LiFePO4 particles. The as-prepared LiFePO4 particles using polyvinyl pyrrolidone (PVP) template with additional one hour calcination at 700°C exhibit characteristics of good crystallinity, uniform size distribution, high capacity and cycling performance. The specific discharge capacities of 141.2 and 114.0mA·h/g were obtained at the charge/discharge rates of 0.1 and 1.0 C, respectively. It retained 96.0% of an initial capacity after 100 cycles at 1.0 C rate. The good electrochemical performance of the as-synthesized material is attributed to the synergistic factors of its reasonable particle size and surface areas and high crystallinity.